I'm periodically seeing this in the error log - does anyone know what the cause may be ? OF 3.5.1 with MoTD plugin on CentOS 5

at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.filterWrite(AbstractIoFilterChain.java:659)
at org.apache.mina.filter.codec.ProtocolCodecFilter.filterWrite(ProtocolCodecFilter.java:205)
at org.apache.mina.common.support.AbstractIoFilterChain.callPreviousFilterWrite(AbstractIoFilterChain.java:361)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1300(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.filterWrite(AbstractIoFilterChain.java:659)
at org.apache.mina.common.IoFilterAdapter.filterWrite(IoFilterAdapter.java:90)
at org.jivesoftware.openfire.net.StalledSessionsFilter.filterWrite(StalledSessionsFilter.java:49)
at org.apache.mina.common.support.AbstractIoFilterChain.callPreviousFilterWrite(AbstractIoFilterChain.java:361)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1300(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.filterWrite(AbstractIoFilterChain.java:659)
at org.apache.mina.common.support.AbstractIoFilterChain$TailFilter.filterWrite(AbstractIoFilterChain.java:587)
at org.apache.mina.common.support.AbstractIoFilterChain.callPreviousFilterWrite(AbstractIoFilterChain.java:361)
at org.apache.mina.common.support.AbstractIoFilterChain.fireFilterWrite(AbstractIoFilterChain.java:355)
at org.apache.mina.transport.socket.nio.SocketSessionImpl.write0(SocketSessionImpl.java:166)
at org.apache.mina.common.support.BaseIoSession.write(BaseIoSession.java:177)
at org.apache.mina.common.support.BaseIoSession.write(BaseIoSession.java:168)
at org.jivesoftware.openfire.nio.NIOConnection.deliver(NIOConnection.java:223)
at org.jivesoftware.openfire.session.LocalClientSession.deliver(LocalClientSession.java:787)
at org.jivesoftware.openfire.session.LocalSession.process(LocalSession.java:262)
at org.jivesoftware.openfire.spi.RoutingTableImpl.routePacket(RoutingTableImpl.java:235)
at org.jivesoftware.openfire.net.SocketPacketWriteHandler.process(SocketPacketWriteHandler.java:53)
at org.jivesoftware.openfire.spi.PacketDelivererImpl.deliver(PacketDelivererImpl.java:48)
at org.jivesoftware.openfire.handler.IQHandler.process(IQHandler.java:51)
at org.jivesoftware.openfire.IQRouter.handle(IQRouter.java:349)
at org.jivesoftware.openfire.IQRouter.route(IQRouter.java:101)
at org.jivesoftware.openfire.spi.PacketRouterImpl.route(PacketRouterImpl.java:68)
at org.jivesoftware.openfire.net.StanzaHandler.processIQ(StanzaHandler.java:299)
at org.jivesoftware.openfire.net.ClientStanzaHandler.processIQ(ClientStanzaHandler.java:79)
at org.jivesoftware.openfire.net.StanzaHandler.process(StanzaHandler.java:264)
at org.jivesoftware.openfire.net.StanzaHandler.process(StanzaHandler.java:163)
at org.jivesoftware.openfire.nio.ConnectionHandler.messageReceived(ConnectionHandler.java:133)
at org.apache.mina.common.support.AbstractIoFilterChain$TailFilter.messageReceived(AbstractIoFilterChain.java:570)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
at org.apache.mina.common.IoFilterAdapter.messageReceived(IoFilterAdapter.java:80)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
at org.apache.mina.filter.codec.support.SimpleProtocolDecoderOutput.flush(SimpleProtocolDecoderOutput.java:58)
at org.apache.mina.filter.codec.ProtocolCodecFilter.messageReceived(ProtocolCodecFilter.java:180)
at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
at org.apache.mina.filter.executor.ExecutorFilter.processEvent(ExecutorFilter.java:239)
at org.apache.mina.filter.executor.ExecutorFilter$ProcessEventsRunnable.run(ExecutorFilter.java:283)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)
at java.lang.Thread.run(Unknown Source)